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Residual charge effects on partial discharges'response to varying sub-kHz voltage frequencies

High Voltage 2023年第3期8卷 622-629页

作者： Cuthbert Nyamupangedengu Tapiwa Venge School of Electrical and Information Engineering University of the WitwatersrandJohannesburgSouth Africa

Partial discharges(PD)are the‘cancer’of electrical insulation.Insulation design and mitigation of PD-induced degradation should be based on good knowledge of PD phenomena.In that regard,a significant body of knowledge has been built up from concerted research across the world in past decades and on various aspects of PD phenomena under various conditions.However,the work is far from being complete as new challenges arise.One such challenge is that electric power equipment insulation is becoming more exposed to non-power frequency voltages.Examples are the proliferation of invertor-based grid-tied renewable energy sources and other technologies such as high-frequency power electronic transformers.Questions that are driving continued research in this regard include the reasons for lack of consensus on the findings on how PD characteristics respond to variations in the voltage frequency.This paper presents results of how residual charge influences PD characteristics'response to voltage frequency changes from 1 to 200 Hz.The study approach is implementing the extended 3-capacitor PD model in MATLAB®Simulink®and validating the findings using the relevant experimental results that are available in literature.The PD type studied is that of an air cavity encapsulated in a polyethylene dielectric.Highlights of the findings are that the extent of the influence of residual charge on PD characteristics depends on the relative magnitude of the residual charge as well as the voltage frequency.The relationships however exhibit non-monotonous trends.Such results further confirm similar findings and conclusions by other researchers and could be signalling the establishment of a more solid knowledge base for design of insulations that operate at non-power frequencies.

关键词： charge insulation finding

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Space charge characteristics of silicone elastomer for device packaging under positive square wave voltage

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High Voltage 2023年第2期8卷 401-411页

作者： Jinqiang Zhang Xuebao Li Zhibin Zhao Xiang Cui State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power UniversityBeijingChina

With the rapid development of power electronic devices towards high voltage and power,the insulation challenges faced by devices have attracted widespread attention.Silicone elastomer is widely used in device packaging as one insulating material,and the study of its insulating properties is helpful to the reliable operation of devices.To this end we obtained the space charge characteristics of silicone elastomer under positive square wave voltage by using the pulse-electroacoustic(PEA)method.Firstly based on the existing research and IEC standards,the selection criteria of the resistance and capacitance parameters of a PEA system for space charge measurement under square wave voltage are given.Through this experimental system,the space charge distribution under the positive square wave voltage with different waveform parameters is obtained,and the influences of the waveform parameters on the space charge accumulation are analysed.The amounts of charges under the action of square wave voltage with different waveform parameters are calculated,and the influences of waveform parameters on the amounts of charges are analysed.In addition,the reasons for the difference in the accumulation of positive and negative charges are explained through Schottky injection model,the synthesis reaction and the infrared spectrum of the silicone elastomer.

关键词： charge wave characteristics

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Surface charge accumulation of post insulator: Dominant charge transition under different conditions

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High Voltage 2023年第6期8卷 1225-1233页

作者： Fangwei Liang Feng Wang She Chen Qiuqin Sun Lipeng Zhong College of Electrical and Information Engineering Hunan UniversityChangshaChina

An insulator surface charge may be responsible for flashover along the insulator surface.In this study,experimental investigations of post insulator surface charge are performed using a variety of voltage,gas type,and gas pressure conditions.Combining the model of surface charge transport,the dominant charge transition is revealed considering gas partial discharge.The results show that hetero‐polar charge accumulates near the high voltage electrodes on the insulator at one atmospheric pressure with an applied DC voltage ranging from-10 to-60 kV.The area ratio of the hetero‐polar charge increases from 23%to 53%.It also generates a reversed polarity of surface charges.Under-20 kV,the surface charge near the grounded electrode gradually becomes homo‐polar charges with the decrease of SF6 in 0.5 MPa SF6/N2 gas mixtures.In this case,the most dominant pathway for charge accumulation is through the insulation gas rather than the insulator.For the 20%SF6/80%N2 gas mixtures,homo‐polar charge speckles appear near the grounded plate electrode when the pressure of SF6/N2 gas mixtures decreases to 0.1 MPa.This means that the partial discharge occurs in gas side under a lower gas pressure.Refer to the presenting findings,the dominant charge transition on post in-sulators is provided as an important reference.

关键词： charge insulator transition

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Study on jet formation behavior and optimization of trunconical hypercumulation shaped charge structure

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Defence Technology（防务技术） 2023年第3期21卷 196-206页

作者： Chao Ge Zhuojun Qu Jin Wang Die Hu Yong Zhang School of Mechatronical Engineering Beijing Institute of TechnologyBeijing100081China

Combining the methods of theoretical,numerical and experimental,this research focuses on the jet formation behavior and optimization of trunconical hypercumulation shaped charge structure.With the three-stage division,formation theory of trunconical hypercumulation shaped charge jet is established based on micro element method.By dimensional analysis,main control parameters are identified and their effect on jet formation are analyzed.Through numerical modelling and orthogonal optimization method,influence of the factors and their levels over the indicators of jet tip velocity and jet length as well as order of the significance of each factor and level are obtained.Penetration experiments of trunconical hypercumulation shaped charge based on the orthogonal optimization reveals its advantage over traditional conical shaped charge structure,and finally determines the optimal influence factor level combination.The research and results would provide useful guide for the design and application of trunconical hypercumulation shaped charge structure.

关键词： structure shaped charge

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Measuring charge Distribution of Molecular Cations by an Atomic Coulomb Probe Microscope

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Chinese Physics Letters 2022年第11期39卷 12-17页

作者：余西涛胡晓青周家琪张馨予赵欣宁贾少奎薛晓睿任殿相李孝开吴勇任雪光罗嗣佐丁大军 Institute of Atomic and Molecular Physics Jilin UniversityChangchun 130012China Institute of Applied Physics and Computational Mathematics Beijing 100088China School of Physics Xi'an Jiaotong UniversityXi'an 710049China

Imaging the charge distributions and structures of molecules and clusters will promote the understanding of the dynamics of the quantum system.Here,we report a method by using an Ar atom as a tip to probe the charge distributions of benzene(Bz)cations in gas phase.Remarkably,the measured charge distributions of Bz^(+)(δ_(H)=0.204,δ_(C)=-0.037)and Bz^(2+)(δ_(H)=0.248,δ_(C)=0.0853)agree well with the calculated Mulliken distributions,and the structures of Bz2 is reconstructed by using the measured charge distributions.The structures of two Bz2isomers(T-shaped and PD isomers)can be resolved from the measured inter-molecular potential V(R)between two Bz ions,and the structures of Bz dimer agree well with the theoretical predictions.

关键词： isomers charge Probe

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Study on partial discharge and charge accumulation characteristics of oil‐pressboard insulation under DC superimposed harmonic voltage

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High Voltage 2023年第6期8卷 1215-1224页

作者： Shuqi Li Qiang Wang Dongxin He Liangkai Wang Qingquan Li Wen Si Shandong Provincial Key Laboratory of UHV Transmission Technology and Equipment School of Electrical EngineeringShandong UniversityJinanChina Zibo City Product Quality Inspection Institute ZiboChina School of Information and Electrical Engineering Shandong Jianzhu UniversityJinanChina

The oil‐pressboard insulation on the valve side of the converter transformer withstands pulsating square wave voltage.The voltage contains lots of DC components and high‐order harmonics,which is likely to cause insulation failures.The partial discharge and space charge experiments of oil‐impregnated pressboard under DC superimposed har-monic voltage are conducted to study the effects of harmonic frequency and DC com-ponents on the discharge and charge accumulation and to explore the correlation mechanism of charge dynamic behaviour and discharge.Firstly,it is found that high‐order harmonic voltage promotes the partial discharge generation,but DC component sup-presses the discharge.Moreover,the charge inside the pressboard is mainly injected in the same polarity and accumulates over time.The space charge density near the electrode increases with the increase of harmonic frequency,and the large amount of charge in-jection leads to electric field distortion.Meanwhile,the electric field direction changes faster,and the frequent charge injection and extraction behaviours make the charge recombination intensify,which promotes the discharge.Through the above analysis,the influence law of harmonic voltage on the failure of oil‐pressboard insulation is obtained,providing a theoretical basis for the structural optimisation and condition assessment of the converter transformer insulation.

关键词： harmonic insulation charge

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Temperature‐dependent adaptive conductivity coating for surface charge release and electric field control under electro‐thermal coupling field

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High Voltage 2023年第5期8卷 1082-1092页

作者： Jianyi Xue Zhu Zhang Binbin Li Yushun Zhao Lijian Ding School of Electrical Engineering and Automation Hefei University of TechnologyHefeiChina Electric Power Research Institute of State Grid Anhui Electric Power Co. Ltd.HefeiChina

Surface charge accumulation is the potential criminal for surface insulation failure on spacers under direct current(DC)voltages.The existence of thermal gradient posing the difficulty of surface charge regulation.This study proposes a temperature‐dependent adaptive conductivity coating technique for surppressing surface charge accumulation under electro‐thermal coupling field.A two‐dimensional axis‐symmetrical simulation model regrading surface charge computation is established.The effects of thermal gradients and coating conductivity on surface charge and electric field distribution are investigated.The results show that the thermal gradient increases the bulk conductive current,therefore aggravating surface charge accumulation.The effects of the coating condcutivity on surface charge and electric field contains three stages.The lower coating conductivity leads to aggravated homo‐polarity charge accumulation.By increasing the coating conductivity,the surface charge and electric field are significantly suppressed at the obtained optimal conductivity,where the bulk and surface conductive current reach a balance stage.Continuously increasing the coating conductivity results in aggravated hetero‐polarity charges.Besides,the increase of thermal gradient to an appropriate extent contributes to the further suppression of surface charge on coated spacers.It is hoped that this study could provide some references for designing highly reliable DC GIL under electro‐thermal coupling field.

关键词： coating charge conductivity

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A cucurbit[8]uril-stabilized 3D charge transfer supramolecular polymer with a remarkable confinement effect for enhanced photocatalytic proton reduction and thioether oxidation

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Organic Chemistry Frontiers 2022年第5期9卷 1327-1335页

作者： Zhuo Lei Qian Li Jian-Da Sun Ze-Kun Wang Hui Wang Zhan-Ting Li Dan-Wei Zhang Department of Chemistry Shanghai Key Laboratory of Molecular CatalysisFudan UniversityShanghai 200438China

A highly water-soluble tetrahedral compound T1 that contains one tetraphenylmethane core and four 2-oxynaphthelene-CH_(2)-4,4’-bipyridinium(NP-CH_(2)-DIPY)side arms has been prepared.Control experi-ments reveal that NP-CH_(2)-BIPY undergoes antiparallel dimerization which is stabilized by two charge transfer interactions with NP as an electron-rich donor and BIPY as an electron-deficient acceptor.

关键词： stabilized charge transfer

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Aromatic self-assembled monolayers with pentafluoro-λ^(6)-sulfanyl(−SF_(5))termination:Molecular organization and charge transport properties

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Nano Research 2023年第5期16卷 7991-8002页

作者： Yangbiao Liu Marc Zeplichal Sonja Katzbach Adrian Wiesner Saunak Das reas Terfort Michael Zharnikov Angewandte Physikalische Chemie Universität HeidelbergIm Neuenheimer Feld 253D-69120 HeidelbergGermany Institut für Anorganische und Analytische Chemie Johann Wolfgang Goethe Universität FrankfurtMax-von-Laue-Straße 7D-60438 Frankfurt am MainGermany

A series of molecules with oligophenylene backbone,thiolate anchoring group,pentafluoro-λ^(6)-sulfanyl(−SF_(5))tail group was synthesized and used as precursors to form self-assembled monolayers(SAMs)on Au(111)substrates.The resulting SAMs feature dense molecular packing,upright molecular orientation,chemically homogeneous SAM-ambient interface,comprised entirely of the−SF_(5)moieties.These SAMs exhibit exceptional wetting and electrostatic properties,showing advancing water contact angles up to 103°and work function values up to 5.96 eV—probably the highest values reported for any aromatic monolayers on gold.They also feature a comparably low value of the tunnelling decay coefficient(0.38±0.07Å^(−1)),typical of oligophenylene backbone,which is not affected by the introduction of the−SF_(5)group.The latter also hardly affects the current densities at a specific bias compared to analogous monolayers with other electronegative tail groups.The superior electrostatic and good charge transport properties of the designed,SF_(5)-terminated SAMs make them potentially useful for interface engineering in organic electronics and photovoltaics.

关键词： backbone charge electrostatic

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Stabilizing charge storage of Fe_(2)O_(3)-based electrode via phosphate ion functionalization for long cycling life

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Rare Metals 2023年第1期42卷 39-46页

作者： Li-Ming Wan Qiu-Ying Xia Jiang-Hua Wu Jing Liu Zheng-Yi Shi Si Lan Teng Zhai Serguei V.Savilov Sergey M.Aldoshin Hui Xia Herbert Gleiter Institute of Nanoscience School of Materials Science and EngineeringNanjing University of Science and TechnologyNanjing210094China National Laboratory of Solid State Microstructures Jiangsu Key Laboratory of Artificial Functional MaterialsCollege of Engineering and Applied Sciences and Collaborative Innovation Center of Advanced MicrostructuresNanjing UniversityNanjing210093China Department of Chemistry M.V.Lomonosov Moscow State UniversityMoscow119991Russian Federation Faculty of Fundamental Physical and Chemical Engineering M.V.Lomonosov Moscow State UniversityMoscow119991Russian Federation

Compositing metal oxides with nanostructured carbon or conductive polymer supports has been regarded as a compelling way to develop electrode materials with enhanced energy density as well as large power in supercapacitors.Yet,the corresponding cycling stability is still greatly limited due to the intrinsic dissolution of metal oxide nanostructures during redox processes.Herein,phosphate ions modified Fe_(2)O_(3) nanoparticles composited with hollow carbon nanosheet arrays have been synthesized as desirable electrodes with both significantly expanded lifespan and high pseudocapacitance.

关键词： electrode expanded charge

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